1. Field of the Invention
The present invention relates to a capacitive sensor, and, more particularly, to a plate type capacitive sensor for five-dimensional displacement measurement that is capable of simultaneously measuring five-dimensional movement of an object, which includes the horizontal movement, the vertical movement, and the tilt of the object.
2. Description of the Related Art
Smart sensor systems, in particular, position measurement systems are expected to play a significant role in the high precision intelligent manufacturing system. For examples, a feedback control is inevitable to ensure the sufficient repeatability for the high resolution positioning of semiconductor manufacturing systems. In addition, usage of active bearings like active magnetic bearings are being increased to achieve the higher precision and productivity. In these systems, the position measurement systems not only affect the system performance but also the system size and complexity.
Capacitive sensors are widely used in short-range ultra-precision and control applications because they have higher resolutions compared with other types of sensors. The greater the ratio of the area of sensor to the distance from the target, the greater the accuracy and resolution of the sensor. In addition, the ratio of sensor area to the characteristic surface finish dimension of the part should be as great as possible to provide the averaging effect.
A plate type capacitive sensor has been developed for use as a measuring device for two-dimensional micro-position control. However, error analysis and design criteria, such as change in distance between the sensor and the object, has not been sufficiently studied, and therefore, this plate type capacitive sensor is hardly used in ultra-precision applications. Cylinder type capacitive sensor was developed and applied to several applications as the CCS is less sensitive to geometric errors and has high resolution with large sensing area. However, the measurement range of the cylinder type capacitive sensor is narrow due to its large nonlinearity and the manufacturing procedure of the cylinder type capacitive sensor is very complicated. Consequently, the cylinder type capacitive sensor is not widely utilized.